Vibration devices are known, with rotating eccentric masses, which are applied on conveying apparatuses of the vibrating or oscillating type, to convey a metal charge to a melting furnace of a steelworks.
It is known that these conveying apparatuses have extremely large overall lengths, in the range of some tens of meters, both to allow a suitable loading plane, so as to guarantee the desired load, and also to define a segment long enough to be able to pre-heat the metal charge while it is being conveyed. Each apparatus must therefore be sized to support a metal charge with a weight of some tens of tonnes.
To support these high loads, known apparatuses each comprise a very heavy bearing structure, even more than a hundred tonnes, on which a vibration device is mounted. Such bearing structures, on the upper part of which a conveyor channel is mounted, are supported by support elements that allow them to oscillate, or vibrate, mainly along their longitudinal axis, while remaining substantially horizontal. The oscillation is conferred by the vibration device associated therewith and allows to feed the metal charge forward inside the conveyor channel.
Known vibration devices, associated with the conveying apparatuses, normally consist of one or more pairs of eccentric masses, rotating in synchrony with each other, to generate a vibrational motion that is transmitted to the bearing structure and the corresponding conveyor channel.
The bearing structure, the conveyor channel and the vibration device thus form a structural combination that has its own frequency of resonance. The longitudinal accelerations imparted to the structural combination by the vibration device cause a corresponding movement of the metal charge with respect to the conveyor channel which feeds it forward to the melting furnace.
The forces generated by the rotating masses of the vibration device must therefore not only be very high, that is, such as to induce an adequate horizontal and alternate force to the structural combination, but also such as to impart on the latter adequate accelerations, in the range of at least 10 m/s2, and also a frequency of oscillation that is considerably different from the forces of resonance of the structural combination, with or without the metal charge loaded inside.
In particular, document WO2006/089865 in the name of the present Applicant discloses a vibration device that is mounted at one end of the conveyor channel and provides to impart on the latter a vibration effect such as to feed forward the mass of metal charge substantially continuously.
This known vibration device comprises two identical vibration mechanisms, disposed laterally and on opposite sides of the support structure of the conveyor channel.
Each vibration mechanism is provided with a pair of eccentric masses that rotate synchronized with each other and in opposite directions of rotation.
Each of the eccentric masses is mounted on rotation shafts having parallel axes of rotation, orthogonal to the direction of feed of the metal charge and disposed substantially vertical, that is, orthogonal with respect to the feed plane of the conveyor channel.
It is also known that, for steelworks which require particular characteristics of the conveyor channel, which imply an overall increase in the latter, due for example to the insulation system or cooling system, the above vibration devices must be able to move high loads. This need requires an increase in the weight of the rotating eccentric masses in order to increase the vibrational effect and consequently the production capacity of the vibration devices.
Each vibration mechanism is provided with a first eccentric mass that is heavier and bigger than a second eccentric mass that is made to rotate synchronized with the first eccentric mass. The first eccentric mass has its mass barycenter disposed angularly offset with respect to the second eccentric mass in order to determine the feed of the metal charge.
It is also known that, in order to guarantee an adequate vibrational effect, the first eccentric masses must be even heavier than two tonnes, and therefore the centrifugal forces that are generated are particularly high, and constitute a factor of fundamental importance for sizing the support elements, such as for example bearings.
It is therefore clear that the mechanical resistance to the stresses of the centrifugal forces due to the support elements is a constraining factor with regard to the sizing of the masses and hence to the efficiency and production capacity of the vibration device.
One purpose of the present invention is to obtain a vibration device that is able to develop a resulting high acting force, and which therefore allows to transfer large loads of metal charge through the conveyor channel.
Another purpose of the present invention is to limit the stresses to which the support elements of the eccentric masses of the vibration device are subjected.
Another purpose is to obtain a vibration device in which the maintenance interventions on its components are reduced.
Another purpose of the present invention is to obtain a vibration device that has limited bulk, at least in the transverse direction with respect to the direction of feed of the metal charge.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.